Heart valve replacement is required when a patient's heart valve becomes diseased or damaged. Surgically implanted heart valve prostheses have extended the life expectancy of many patients with defective heart valves. Such prostheses can be either mechanical or biological (tissue valves), stented or stentless, and may be implanted into an aortic, mitral, tricuspid, or pulmonary position.
During a surgical procedure, the heart is typically stopped and the patient attached to a heart/lung bypass machine that pumps and oxygenates the patient's blood. The longer a patient is required to rely on the artificial heart/lung bypass machine to maintain vital functions, the greater the stress on the patient. There is consequently a need to simplify the surgical implantation of a heart valve prosthesis into the implantation annulus in order to minimize both the length of surgery and the amount of time spent on heart/lung bypass.
Stented heart valves made from flexible material or from materials that exhibit shape memory characteristics promise less complicated and faster valve implantation procedures. The stents supporting the heart valves are generally cylindrical in shape and are structured to be crimped so as to reduce their size for delivery to a target site. The stents may be either self-expanding or non self-expanding. Self-expanding stents may be formed from any suitable shape memory material, such as Nitinol. Non self-expanding stents are typically expanded via an inflation means or mechanical expansion means. Stented heart valves are sometimes referred to as suture-less valves because they may be implanted and secured into the annulus without the use of sutures.
As appreciated by those of ordinary skill in the art, it is desirable to crimp or otherwise radially compress the stent in a substantially uniform manner to minimize the variation in pressures applied to the stent. Such pressure variations may lead to deformation of the stent, which may reduce the ability of the stent to securely maintain the heart valve at the target location. Thus, if a stent is crimped in a non-uniform manner, it is typically either re-crimped or thrown away. Re-crimping of stents is not desirable because the repeated application of force on the stent may cause fatigue or weakening of the stent structure. Disposing of poorly crimped stents is also not desirable due to the increased costs associated with the waste. This is especially true with stented heart valves because the stent and the heart valve are attached together and must be disposed of as a single unit.
A number of different strategies have been used to repair or replace a defective heart valve with a stented replacement valve. Generally speaking, open-heart valve repair or replacement surgery involves a gross thoracotomy, usually in the form of a median sternotomy. In this procedure, a saw or other cutting instrument is used to cut the sternum longitudinally and the two opposing halves of the anterior or ventral portion of the rib cage are spread apart. A large opening into the thoracic cavity is thus created, through which the surgeon may directly visualize and operate upon the heart and other thoracic contents. The patient must be placed on cardiopulmonary bypass for the duration of the surgery. Open-chest valve replacement surgery has the benefit of permitting the direct implantation of the replacement valve at its intended target site. For example, the crimped stented replacement valve may be delivered to the target site with a delivery catheter or the like. Once positioned in the desired location, the stent may be re-expanded or self-expands to secure the replacement heart valve in place by exerting radial forces against the internal walls of the implantation annulus.
New delivery devices and methods which make the surgical procedure more efficient and minimize the length of time of the procedure are always needed. Furthermore, new delivery devices and methods which provide the surgeon with improved visualization of the stented heart valve during delivery as well as improved control over the deployment of the stented heart valve are also needed.